1. Field of the Invention
This invention relates to a stacker for stimulable phosphor sheets which is provided in a conveyance path of a sheet conveyance means for conveying stimulable phosphor sheets in a radiation image read-out apparatus and which is capable of temporarily housing a plurality of the stimulable phosphor sheets therein and feeding out the housed sheets one by one. This invention particularly relates to a stacker for stimulable phosphor sheets which does not cause the radiation image read-out apparatus to become large.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318 and 4,387,428 and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet or simply as a sheet) is first exposed to a radiation passing through an object such as the human body to have a radiation image of the object stored thereon, and is then scanned with stimulating rays such as a laser beam which cause it to emit light in proportion to the stored radiation energy. The light emitted by the stimulable phosphor sheet upon stimulation thereof is photoelectrically detected and converted to electric image signals, and the radiation image of the object is reproduced as a visible image by use of the image signals on a recording material such as a photographic film, a display device such as a cathode ray tube (CRT), or the like.
In the aforesaid radiation image recording and reproducing system, the stimulable phosphor sheet is used to temporarily store a radiation image until the sheet is scanned with stimulating rays to read out the radiation image. Therefore, after the radiation image is read out from the stimulable phosphor sheet, radiation energy remaining thereon should be erased to reuse the sheet.
For satisfying this requirement, besides a radiation image read-out apparatus consisting of a read-out section for reading out an image stored on a stimulable phosphor sheet, there has heretofore been proposed a radiation image read-out apparatus provided with the read-out section and an erasing section for erasing radiation energy remaining on the sheet.
In the proposed radiation image read-out apparatus, a cassette housing a stimulable phosphor sheet carrying a radiation image stored thereon by use of an external image recording apparatus is generally fed to a cassette holding section. The stimulable phosphor sheet is taken out of the cassette, transferred to a sheet conveyance means, and conveyed by the sheet conveyance means to the read-out section. Also, in general, a stacker for temporarily housing a plurality of the stimulable phosphor sheets, feeding out the sheets one by one and transferring them to the sheet conveyance means is provided in the conveyance path between the cassette holding section and the read-out section. Specifically, a comparatively long time is taken for carrying out image read-out at the read-out section. Therefore, in the case where the stacker is provided, a plurality of image-recorded stimulable phosphor sheets can be introduced into the radiation image read-out apparatus while the image read-out is being carried out for a single stimulable phosphor sheet at the read-out section, and it is possible to eliminate the problem that the image-recorded sheet is made to wait for a long time in the form housed in the stacker at the cassette holding section. Also, in the case where the stacker is provided, even though the read-out section becomes defective and inoperable, image recording in an external image recording apparatus need not be stopped immediately, but instead the image recording apparatus can be operated continuously for some period.
On the other hand, in the radiation image read-out apparatus provided with the read-out section and the erasing section as mentioned above, the stimulable phosphor sheet on which the erasing has been finished at the erasing section is taken out of the read-out apparatus and reused for image recording. In general, a plurality of the erased reusable sheets are stacked in a stacking tray inside of the read-out apparatus, and taken out of the read-out apparatus in the form housed in the stacking tray. Since the sheets stacked in the stacking tray should be housed one by one in a cassette as mentioned above when they are to be reused for image recording, it is necessary to load the sheets one by one into a cassette prior to image recording. Therefore, a long time is taken for housing each sheet ready for image recording into a cassette and conducting image recording on the sheet, and it is not always possible to efficiently circulate and reuse the sheet. Also, though loading of the sheet into the cassette is carried out by use of a special-purpose loader or manually, the cost of the overall system increases in the case where the special-purpose loader is used, and manual loading is disadvantageous from the viewpoint of sheet processing since the sheet must be manually touched directly. The radiation image read-out apparatus may also be constituted so that the sheet is circulated therein, taken out of a cassette afterimage recording, subjected to image read-out and erasing, and then conveyed and housed in a cassette. However, with such a read-out apparatus, since the read-out apparatus is exclusively occupied by a single sheet until the sheet is housed in the cassette after image read-out and erasing are conducted on the sheet, processing of the next sheet cannot be started as long as processing of the preceding sheet is being conducted. Thus an unnecessarily long time is taken, and the processing capacity of the apparatus decreases markedly. Accordingly, in the radiation image read-out apparatus provided with the erasing section, it would be very advantageous if a stacker for temporarily housing the sheets therein and feeding out a single desired sheet among the housed sheets could be provided in the sheet conveyance means present on the downstream side of the erasing section.
Accordingly, in Japanese Patent Application No. 61(1986)-16074, the applicant proposed a stacker which is adapted to provision between a sheet feeding section such as a cassette holding section and a read-out section or between an erasing section and the cassette holding section, and which enables classification of the housed stimulable phosphor sheets in accordance with the sheet size and preferential feed-out of a specific sheet.
With reference to FIG. 16, the proposed stacker is disposed in a sheet conveyance means 450 and is provided with a tray unit 410 comprising a plurality of trays 411, 411, . . . each of which can house a single stimulable phosphor sheet therein. The tray unit 410 is moved by a unit movement means (not shown) in the direction as indicated by the arrow between the position as indicated by the solid line and the position as indicated by the chain line so that an arbitrary tray 411 faces the feed-in rollers 421 and 422 provided above the tray unit 410 and the feed-out rollers 431 and 432 provided below the tray unit 410. At the time the stimulable phosphor sheet is to be fed into the tray 411, the inclination of the tray 411 for receiving the sheet is changed so that the space between said tray 411 and the tray adjacent thereto increases. At the time the stimulable phosphor sheet is to be fed out of the tray unit 410, the tray 411 housing the sheet which is to be fed out is moved to the position above the feed-out rollers 431 and 432, a bottom plate 413 of the tray 411 is opened, so that the sheet is allowed to fall from the tray 411 and is transferred to the feed-out rollers 431 and 432. With the stacker constituted in this manner, each sheet is fed into an arbitrary tray, and an arbitrary sheet can be fed out of the tray unit 410. Therefore, a specific sheet can be fed out of the tray unit 410 and processed preferentially. Also, the sheets can be housed in the trays 411, 411, . . . by being classified in accordance with the sheet size, and a sheet of a required size can be fed out of the tray 411. Further, the stacker is adapted to the provision between the sheet feeding section and the read-out section or between the erasing section and the cassette holding section.
However, with the aforesaid stacker, each tray 411 is held in the condition inclined obliquely in order to facilitate feed-in and feed-out of the stimulable phosphor sheet and to support the sheet reliably. In the case where the movement range of the tray unit 410 is from the position as indicated by the solid line to the position as indicated by the chain line in FIG. 16, the width in the direction of the stacker movement which is required for moving the stacker is determined by the position P1 and the position P2 shown in FIG. 16. Therefore, in order to provide the stacker, it is necessary to provide a comparatively large space as compared with the width of the stacker itself, and the radiation image read-out apparatus as a whole becomes large.